Luis is 4 times as old as Michael and is also 6 years older than Michael. How old is Michael?
Solution: We can use the given information to write down two equations that describe the ages of Luis and Michael. Let Luis's current age be $l$ and Michael's current age be $m$ $l = 4m$ $l = m + 6$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $m$ , and both of our equations have $l$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4m$ $-$ $ (m + 6)$ which combines the information about $m$ from both of our original equations. Solving for $m$ , we get: $3 m = 6$ $m = 2$.